The present invention relates to a technique for monitoring the eye movements of a subject wearing eyeglasses, and in particular to a light, unobtrusive device easily and removably mountable on any conventional eyeglass frame.
Equipment that can monitor the eye movements of a person in response to certain visual stimuli is well known. Typically, the subject would be exposed to a visual stimulus and his ocular reactions recorded by a monitoring apparatus. Such an apparatus can include a light source, visible or infrared, which is bounced off the eye into a suitable detector. The detected signal is then electronically processed to obtain a reading of the eye position at any given time. Various such technologies are discussed in the article "Methods and Designs, Survey of Eye Movement Recording Methods" by Lawrence R. Young and David Sheena in the publication Behavior Research Methods and Instrumentation 1975, Vol 7(5) pgs. 397-429.
Many applications exist for such an apparatus; these include medical diagnosis, military uses such as weapons aiming, training equipment such as aircraft simulators, sports analysis for improving visual techniques and concentration, advertisement testing, design planning as for an automobile dashboard, and testing for visual impact as of highway and store signs. In some of the listed applications, medical diagnosis and aircraft simulators for example, the eye-movement-monitoring apparatus is stationary, as is the equipment for presenting the visual stimuli, such as a video monitor. Since the latter two are fixed, the viewer is also stationary. Typically, the subject is seated and his head fixed in place by a chin rest or a bit plate. However, in some applications, the exposure to the requisite stimuli requires movement. Thus, if analysis of a baseball batter's vision as he watches a pitched ball is desired, it would be preferable to actually do that in a batter's box in a realistic situation. Likewise, in advertising applications a subject may be requested to walk down a supermarket aisle so that his response to the most eye-catching containers can be recorded. Stationary equipment obviously cannot accomplish such tasks.
Head-mounted eye-movement-monitoring equipment has been devised which obviates the need to keep the person's head fixed. Since the equipment is affixed to the subject's head, it moves with his head and provides an accurate signal regardless of how he moves it. Such devices have been used in, for example, military applications where head movement is essential (e.g. the helmet of a pilot) and even in applications where head movement is not essential but preferable. As regards the latter, a fixed position for the head is to be avoided when the monitoring session is relatively lengthy because the subject is likely to experience considerable discomfort after awhile and a commensurate decrease in concentration. Various head-mounted arrangements are available. For example, U.S. Pat. No. 4,102,564 issued July 25, 1978 to Henry L. Michael discloses a type of arrangement including light sources and sensors mounted on a helmet. U.S. Pat. No. 3,473,868 issued Oct. 21, 1969 to Young et al. discloses a spectacle frame used in eye glasses. On the frame are mounted a light source and detectors to sense the light reflected by the eye to provide horizontal and vertical eye movement measurements. However, no provision is made for specific lens prescriptions in order to make it usable by many subjects. Also, the frame is specially modified by supports secured permanently to it to carry the monitoring devices.
My U.S. patent application Ser. No. 486,031 filed Apr. 18, 1983 discloses apparatus which is advantageously usable for eyeglass wearers. An eyeglass frame is modified to include clips for removably retaining corrective lenses. As described in that application, the corrective prescription of the subject is determined and appropriate lenses are selected from a stock kept on hand at the testing site. The eyeglass frame is further modified by an arrangement for adjustably carrying the light source and eye movement detector on the frame. These are permanently affixed to the frame.
Although the arrangement described in the above-mentioned patent application is a substantial improvement over previously known devices in that it provides a light, highly portable means which is readily modifiable to the subjects's prescription, it nevertheless has several disadvantages. For example, a stock of corrective lenses must be kept on hand. Also, since only a reasonable number of such lenses can be kept readily available, the subjects's precise correction may not be available in which case only the closest available prescription will be selected. However, this may cause the subject some degree of distraction. Furthermore, since the light source, eye movement detector and scene monitor are affixed to a frame used for all subjects, a particular subject cannot use his own frame. The standard frame he must use may cause the subject some discomfort and may, thus, be the source of additional distraction.
For specific applications, regardless of whether stationary or head-mounted equipment is used, it is desirable to superimpose the subject's eye movements on the viewed scene. This, of course, requires not only eye movement monitoring equipment but also apparatus for simultaneously detecting the scene being viewed. Signals from the eye-movement-monitoring equipment and the scene detection devices are electronically combined to attain the desired superimposition. Thus, in the above-described sports situation, the batter's eye movements would be superimposed on a scene showing approach of the pitched ball toward him. Analysis is thus possible of whether he is looking properly at the ball. In advertising, a subject is shown a filmed advertisement. Both his response and the ad are monitored. Combining the two enables the determination of the portions of the advertisement to which the subject's eyes are drawn and, thus, an analysis is possible of the effectiveness of the advertisement in attracting the subject's attention, causing him to look at the desirable portions, and creating a lasting impression. See for example my U.S. Pat. No. 4,075,657 issued Feb. 21, 1978.
Equipment exists for accomplishing both aims of portability and recordal of the viewed scene. See, for example, U.S. Pat. No. 3,542,457 issued Nov. 24, 1970 to Balding et al. It discloses two helmet-mounted television cameras. One camera records an eye spot generated by an optical system for monitoring eye movement. The other camera is aimed at the scene being viewed. Signals from the two cameras are mixed to obtain the requisite superimposition. However, this and systems like it suffer from several disadvantages. The bulk and weight of the equipment can cause discomfort and fatigue. Also, the equipment blocks the vision of one and eye and reduces peripheral vision in the other. This interferes with depth perception and is a constant reminder of the test situation and can, therefore, result in distorted responses. Eyeglass wearers cannot use the equipment because the lenses can distort the light from the optical monitoring equipment and since the apparatus leaves too little clearance to accommodate glasses. In addition, such equipment cannot readily be calibrated for the eye shape of individual subjects.
The invention applies the corneal reflection method to monitor eye movement. (See the above-mentioned Young and Sheena article). Eye movement monitoring techniques using the corneal reflection method must deal with another source of inaccuracy caused by the irregular shape of the eye. In calibrating the testing apparatus used in implementing such a technique, the subject is asked to look in the center of the displayed scene which may be on a video monitor for example, and the signal picked up from his eye with this monitoring equipment is adjusted so that the resulting dot appears in the center of the video monitor. Thus, the place where the subject is looking and the dot generated by the monitoring equipment are made to coincide. The subject is then asked to look at the upper right hand corner of the displayed image, and the apparatus is calibrated, as by operating a zoom lens, to place the signal detected from the eye at the upper right hand corner of the video monitor. In this manner, the monitored range of eye movement is adjusted so it is equivalent to the size of the scene being viewed by the subject. Were the subject's eye perfectly spherical, eye motion to the lower left hand corner of the displayed scene would accordingly place the resulting signal at the corresponding corner of the monitor. However, due to the imperfect shape of the eye, this usually does not occur. Thus, a correction must be provided so that eye motion to any part of the screen is correctly and accurately detected, recorded and interpreted despite the distinct eye imperfections of individual subjects.